(1) Field of the Invention
The present invention relates to a fluid control valve that adjusts a flow rate of fluid introduced from an upstream side thereof to allow the fluid to be delivered downstream.
(2) Description of the Related Art
Conventionally, a solenoid valve is known which is disposed in a flow passage of fluid for adjusting a flow rate of fluid introduced from an upstream side thereof to allow the fluid to be delivered downstream (see e.g. Japanese Unexamined Patent Publication (Kokai) No. 2002-372164).
Generally, the solenoid valve of this type comprises a solenoid that actuates a valve element for opening and closing operations, and a valve mechanism that opens and closes a flow passage using the valve element. The solenoid includes a solenoid coil to which control current is externally supplied, a core that is fixed, as a fixed core, to the solenoid coil along the axis thereof, a plunger that is axially movably disposed, as a movable core, along the axis of the solenoid coil for operating in unison with the valve element, and a spring that urges the plunger in the valve-opening direction or in the valve-closing direction when the solenoid coil is deenergized. Further, the valve mechanism includes two ports formed in the body, a valve seat that is disposed in a flow passage connecting between the ports and integrally formed with the body, and a valve element that is disposed in a manner opposed to the valve seat and actuated together with the plunger for opening and closing operations.
The solenoid valve has energization of the solenoid controlled to control the lift amount of the valve element from the valve seat to thereby adjust the flow rate of fluid allowed to be delivered downstream.
By the way, the valve element of such a solenoid valve is controlled to move to a position where pressure received from fluid (fluid pressure), an urging force of a spring, and an electromagnetic force generated by the solenoid are balanced. However, as the lift amount of the valve element from the valve seat is increased, there occurs a phenomenon in which an area at which the valve element actually receives pressure (effective pressure-receiving area) decreases, which changes the lift of the valve element and the balance of pressure, resulting in the degraded accuracy of flow rate control of the fluid.
It is considered that the above problems occur not only in the solenoid valve which electromagnetically actuates the valve element but also in a fluid control valve which adjusts the lift amount of the valve element using only the balance between mechanical mechanisms, such as a spring, and the fluid pressure.